Thief hatches are hatches mounted to tanks or other fluid containing vessels that often serve the dual purpose of (1) providing access to the contents of such tanks or vessels to thieve or extract samples, measure levels, and/or take other measurements of the contents of the tanks or vessels, and (2) regulating the pressure within such tanks or vessels. Such hatches provide access to the contents of a tank by a cover or lid that may be pivoted about a hinge to an open position, thereby uncovering an aperture in the tank. Some thief hatches regulate pressure in a tank by releasing pressure when the tank pressure exceeds a high pressure threshold and introducing pressure into the tank when the tank pressure drops below a vacuum pressure threshold (e.g., a negative pressure threshold relative to the ambient atmosphere). When the tank pressure is between the high pressure threshold and the vacuum pressure threshold, seals in the closed hatch reduce (e.g., prevent) leakage of fluid out of the tank. While suitable to any application, such pressure regulating hatches are often implemented on tanks in which volatile and/or vaporizable liquids are stored, transported, or otherwise handled.